1. Field of the Invention
The present invention relates in general to piston crank mechanisms for a reciprocating type internal combustion engine, and more particularly to a lower link of the piston crank mechanisms of a double link type.
2. Description of the Related Art
Hitherto, for connecting pistons of an internal combustion engine to a crankshaft of the same, various piston crank mechanism have been proposed and put into a practical use. Some of them are of a double link type, such as those disclosed in Laid-open Japanese Patent Applications (Tokkai) 2001-227367, 2002-61501 and 2000-54873. In the double link type piston crank mechanism of the published Applications 2001-227367 and 2002-61501, a lower link is employed through which an upper link pivotally connected to a piston through a piston pin and a crank pin of a crankshaft are pivotally connected. The pivotal connection between the lower link and the upper link is made through an upper pin. A control link is further employed which has one end pivotally connected to a fixed portion of an associated engine and the other end pivotally connected to the lower link. In the double link type piston crank mechanism of the other published Application 2000-54873, a control link is pivotally connected to an upper link, not to a lower link. That is, the mechanism comprises an upper link pivotally connected to a piston through a piston pin, a lower link pivotally disposed on a crank pin of a crankshaft and pivotally connected to the upper link, and a control link having one end pivotally connected to a fixed portion of an associated engine and the other end pivotally connected to the upper link.